A heart is the center of a person's circulatory system. It includes a complex electromechanical system performing two major pumping functions. The heart includes four chambers: right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The left portions of the heart, including LA and LV, draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart, including RA and RV, draw deoxygenated blood from the body organs and pump it to the lungs where the blood gets oxygenated. These mechanical pumping functions are accomplished by contractions of the heart. In a normal heart, the sinus node, the heart's natural pacemaker, generates electrical signals, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite the muscular tissues of these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the various portions of the heart to contract in synchrony to result in efficient pumping functions. A blocked or otherwise abnormal electrical conduction and/or a deteriorated myocardium cause asynchronized contraction of the heart, and results in poor hemodynamic performance including diminished blood supply to the body.
Heart failure is a clinical syndrome or condition where the heart fails to supply sufficient blood to meet the metabolic needs of the body organs. It is characterized by (1) signs and symptoms of intravascular and interstitial overload, including shortness of breath, rales, and edema, or (2) manifestations of inadequate tissue perfusion, such as fatigue or poor exercise tolerance. Congestive heart failure (CHF) occurs when heart failure patients further manifest pulmonary or systemic congestion. Measurement of left ventricular performance is a critical step in evaluating and managing cardiac conditions for most heart failure patients. A specific example of heart failure is associated with left bundle branch block (LBBB), where portions of the electrical conduction system activating LV are dysfunctional. LBBB is associated with asynchronous ventricular contraction patterns and depressed ejection fraction, and is inversely correlated to the hemodynamic performance, particularly global contractile function.
Cardiac resynchronization therapy (CRT) with LV or biventricular (BV) pacing has been introduced as a complementary treatment for patients with congestive heart failure and ventricular conduction delay. CRT has been shown to improve LV systolic function as measured by peak positive LV pressure change (dP/dtmax) and Doppler echocardiography. It improves clinical symptoms of heart failure. CRT is believed to improve global ventricular function by restoring more synchronized contraction patterns, which include intraventricular synchrony. Thus, the efficacy of CRT and/or particular CRT parameters is indicated by improved ventricular synchrony.
For these and other reasons, there is a need for quantifying intraventricular asynchrony.